randomly looking for gantry builds as im getting ideas to make mine and i found this. Not trying to critique, but here is an fyi as you said you do your heavy lifting from the edge: When you are not lifting from the middle, you are not loading each support leg evenly. so a 2T load lifted 5 feet from the vertical support would place 3k lbs on the closer side, and then obviously 1k on the other. that would over load the 2400 lbs worth of load capacity (4x600lbs) you have in casters on the closer side, assuming they are all evenly loaded that is too. now factor the weight of the gantry, you are defiantly eating into the factor of safety built into those.
While watching this I came to the same conclusion as you. It worried me when he was talking of lifting thousands of pounds with those wheels. A few years back I had a wheel failure on a temporary square trolley that I made to move a heavy machine. The 4 wheels were at each corner of the square trolley and, in theory, all 4 wheels together were enough to carry the weight of the machine. When moving the trolley and machine over an uneven surface, the weight of the load was shifted over to one corner of the trolley, which overloaded a wheel and caused it to break. That was a pain to rectify!
